Diaphragm for acoustic apparatus



1933- .1 LEOPOLD v DIAPHRAGM FOR ACOUSTIC APPARATUS Filed Dec. 23, 1931D Y L w Wu m Z R N L T E V A W M w AY OB J say, around 2-3 cycles soPatented July 11, 1933 UNITED STATES PATENT orrlca JOACHIM LEOPOLD, OFBEBLIN-OHARLOTTENBURG, GERMANY, ASSIGNOR T0 SIEMENS & HALSKE,AKTIENGESELLSCHAFT, OF SIEMENSSTADT NEAIt BERLIN, GERMANY, A

CORPORATION OF GERMANY DIAPHRAGM FOR ACOUSTIC APPARATUS Applicationfiled December 23, 1931, Serial No. 582,729,

This invention relates to a diaphragm for acoustic apparatus. Moreparticularly it relates to a diaphragm distinguishes itself by a veryuniform and regular reproduction over the whole frequency range.

Several ways and means have been suggested to insure uniformreproduction independcnt of the frequency. I One fundamental principlein this direction has been to choose the natural period of the diaphragmvery low, that such higher harmonics as may arise will come to lie soclose together inside the frequency band that no resonance points willbecome noticeable any longer. Another solution has been to make thediaphragm so stiff that it would oscillate as a rigid body inside theaudible ranges, and to incidentally place the natural frequency of thesystem which essentially is dependent upon the mass of the diaphragm andthe size of the elastic restoring forces, in the neighborhood of 3070cycles. In this manner the occurrence of resonance peaks inside thefrequency band is reduced to a minimum. Now, the last mentioned problemgenerally is frustrated because it is technically impossible to make adiaphragm having a diameter of over 10 cm of the requisite lightness sothat it will oscillate as a rigid body inside the audible range (below10,000 cycles). For instance, attempts have been made to attain thedesired end by cutting portions of a metallic cone away so that thereresults a support or skeleton adapted to serve as a support for a coneof thin paper, silk or similar light material. Apart from the fact thatit is technically and practically unfeasible to make comparatively largediaphragms which will be rigid inside the audible range, there is thedraw-back that because disposition of the recesses or cut-out portionsthe diaphragm exhibits certain preferential natural periods wherebyuniform reproduction and thus sufficient width of the frequency band areunattainable. Another draw back is the relatively great weight whicheven with the use of light metals renders the sensitiveness of thediaphragm rather low.

'lfhe present invention solves the problem for loud speakers which 'uralperiod,

of the special and in Germany April 10, 1931.

in another way. the diaphragm is made so non-rigid that it will notexhibit any single outstanding natbut that it is divided into aplurality of oscillation regions characterized by partial naturalperiods dissimilar from each other. The material from which thediaphragmis made consists preferably of paper According to the invention3 or some other fibrous substance impregnated with synthetic resins; andin this material gaps are cut out which in contradistinction to knownarrangements are irregularly distributed over the whole surface. Theresultant holes are closed by a varnish or gelatinous coating. Bysuitable diaphragm construction in conjunction with proper selection ofthe holes or cut-outs, it is thus feasible to influence the frequencycurve of the loudspeaker throughout the entire frequency range in such away that the natural periods of vibration will no longer exercise atroublesome effect. Another advantage of the new diaphragm is thereduction of the volume or mass of the diaphragm with the active surfaceor area being the same. Bv breaking up the continuity of the diaphragmsurface, with the resultant gaps, however, being re-closed by saidcoating, the diaphragm according to the arrangement of the breaks orcut-outs, is provided with different partial masses and partialelasticities so that certain resonance points which invariably arise indiaphragms of larger dimensions are shifted or diminished by theprovision of the gaps. In the case of a cone could be disposed annularlyand concentrically in reference to the base circle of the cone so thatthey will fulfill a problem and object similar to the ribs or finsconcentric and annular in reference to the base circle of the cone andpressed into the diaphragm material. However, the advantage oifered bythe said gaps or breaks compared with the said annuli is that themechanically similar constructure is obtainable with less diaphragmmaterial or substance when recourse is had to the breaks or gaps. Thediaphragm is thus endowed with numerous surface parts which possessdifferent natural periods so that a wide frequency band will bereproduced at satisfactory efiiciency.

By a number of experiments and by cal culation the required partialmasses and partial elasticities are ascertainable with comparative ease.Inasmuch as it is worth while making the diaphragm weather-proof re-'course is had to a sort of varnish which possesses weather-proofproperties and which will be stable also to chemical actions such asproduced by acid fumes.

By the use of the idea underlying the invention it is possible tomanufacture a diaphragm the production of which is free from anytechnical difficulties while yet offering extremely good conditions asregards faithful reproduction. The mass of the diaphragm, and therequisite stiffness are governed by the size, number and disposition ofthe cut-outs or breaks.

The drawing shows embodiments of the basic idea of the invention by wayof example, the figures relating more particularly to cone typediaphragms, though it will be evident that the idea could be appliedalso to any other diaphragm. Fig. 1 illustrates one embodiment of theinvention. Figs. 2 and 3 illustrate modifications.

Fig. 1 clearly shows the arrangement of the recesses. The material ofthe cone 1 consists of paper impregnated with synthetic resin; the gapsor cut-out portions 2 are covered with weather and acid-proof varnish.In this manner the weight of the new diaphragm compared with a diaphragmhaving the same active surface of material such as paper, is diminished.At the same time the advantage of a more uniform reproduction throughoutthe entire frequency band is attained.

Fig. 2 shows a cone diaphragm with annular concentric gaps 3. In orderthat the form of the diaphragm may be preserved in this case it isadvisable to make the annuli or cut-out portions not entirely annular,but to leave some material at certain points designated by 4 in thedrawing.

in the embodiment Fig. 3 the same purpose is obtained by round recessesor cut-outs disposed annularly while the distances between the rings mayincrease in the direction of the margin or border.

The gaps may be so arranged that the partial masses grow toward theedge, a feature that is desirable and advantageous for betterreproduction of the low pitches. This end is attained, for instance, ifin annular and concentric arrangement of the breaks their distance andtheir width remain constant from the inside toward the outside, or elseif this distance is increased from the inside toward the outside.

The yieldingness of the diaphragm is increased if the angle of openingof the cone is larger than 90 degrees seeing that the rigidity of thecone increases as the angle of the aperture decreases, aproperty that isto be avoided according to the invention.

What I claim is:

1. A diaphragm comprising a sheet of nonrigid material in which aplurality of irregularly sized and irregularly distributed gaps are cutout over the entire surface.

2. A diaphragm of fibrous substance impregnated with synthetic resinsand provided with a plurality of irregularly distributed openingscovered with a hardened weatherproof and acid-proof solution.

3. A diaphragm comprising a sheet of fibrous material impregnated with astiffening material, a plurality of irregularly distributed andirregularly sized openings in said diaphragm material and a substancedifferent from that of the diaphragm material for closing said opening,said substance being of less mass than the material removed from saidopenings and being substantially weather and acid proof.

4. A diaphragm comprising a sheet of perforated material, saidperforations being of different sizes and shapes and irregularlydistributed over the diaphragm surface and a gelatinous coating closingsaid perforations.

5. A conical diaphragm provided with a plurality of angularly andconcentrically disposed openings and a substance of different, materialfrom "that of the diaphragm for filling said perforations, saidsubstance being of a gelatinous nature and of less massthan the materialremoved in forming said openm s.

Tn testimony whereof I afiix my signature.

JOACHIM LEOPOLD.

